A MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) is used as a switching element of an electronic circuit, such as an inverter circuit or a converter circuit. A PN junction diode (body diode) that is a bipolar device parasitizes the MOSFET. In an electronic circuit in which the MOSFET is used, there is a fear that, if an electric current flows through the PN junction diode (body diode) parasitizing the MOSFET, device properties will be deteriorated. In detail, if an electric current flows through the PN junction diode, and if the MOSFET has a crystal defect area, there is a fear that an electron and a hole will be recombined together in the crystal defect area, and the crystal defect area will be enlarged.
Especially in an SiC MOSFET made or an SiC-based semiconducting material, if an electric current flows through a PN junction diode, a forward direction deterioration (hereinafter, referred to simply as a “forward deterioration”) will be caused. In more detail, it is known that an SiC semiconductor crystal has a crystal defect that is called “BPD (Basal Plane Dislocation).” The crystal structure of a BPD part is characterized in that the band gap of its crystal is smaller than the original band gap of an SiC semiconductor, unlike the crystal structure of the other parts. Therefore, the BPD part is liable to become a recombination center of an electron and a hole. Therefore, if a forward current flows through a PN junction part, BPD will be enlarged, and will cause a stacking fault. As a result, the on-resistance of the SiC MOSFET will be increased.
Therefore, in order to prevent an electric current from flowing through the PN junction diode, a proposal has been made to provide a circuit structure in which a Schottky barrier diode whose operating voltage is lower than that of the PN junction diode is connected in parallel to the PN junction diode.